Download ENV Ch 7 Popul Prin.doc

August 2012
Environmental Science Ch # 7
POPULATIONS – Characteristics and Issues.
Characteristics
Natality- Asexual
Sexual
Mortality (View Survivor Curve)
Population Growth Rate (Births – Deaths)
Sex ratios
Age Distribution (Pre- reproductive/Reproductive/ Post-reproductive)
Population Density and Spatial Distribution
Emigration
Immigration
Culture change/introduction of new Characteristics/ diseases
A Population Growth Curve
Pattern (Lag/Exponential/Stable/ Crash)
Factors that Limit Population Size
No increase indefinitely
Intrinsic – behavior changes
Extrinsic – Out side forces : predators/ lack of sunlight.
Density dependent – factors that become more effective with growth.
Density independent – not related to population density, accidental factors.
Categories of Limiting Factors
Raw materials availability
Energy
Waste generation and disposal
Interactions among organisms
Carrying Capacity – Definition.
Reproductive Strategies and Population Fluctuations.
“K” Strategists – density dependent factors
“r” Strategists – density independent.
Fluctuations – due to natural resources availability , short term
Population Cycles – heavy feeding/ predator population.
Human Population Growth – Calculating growth 70/growth rate.
Human Population Characteristics and Implications
Economic Developed Countries – 3% growth by 2050
Less developed – 52%
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World 86% in Undeveloped
Envir. Impact of a population – growth tied to economic development
& Envir Problems.
Factors that influence Human Population Growth
Biological
Social
Economic
Political.
Population Growth Rates and Standard of Living
Concept based on Economic well-being; health; ability to change
status. GNP,( internal production and purchasing power.)
Hunger food Production and Environmental Degradation
Food production
Environmental impact of food production
Human energy pyramid
Economics and politics of Hunger
Demographic Transition Concept
US Population Picture
Immigration policy
What does the Future hold?
Available raw materials
Available energy
Waste Disposal
Interactions
Social factors/ freedom of choice
Ultimate size - limitations
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7 – 1. Characteristics
Genetic Differences - Populations: a group of individuals of the same species inhabiting
an area. Specific characteristics distinguish one population from another.
** Natality – Birth rate. The # added to a population as a result of reproduction over a
specific time period.
Asexual reproduction: Bacteria reproduce when divided. So do some plants and
animals, or budding off small portions of themselves. Some insects and lizards lay
unfertilized eggs, that are identical genetically to the female.
Sexual reproduction: Plants produce seeds, but those seeds must land in a
appropriate soil before they will germinate.
In human populations, natality is measured in the number born/1000/year.
In most other species, reproduction is very high. More offsprings are produced than are
needed to replace parents or can survive.
** Mortality – death rate. The # of deaths over a particular time period. In Human
species, death rate is measured in #/1000/year. To grow, a population requires a birth rate
greater than death rate.
A 2nd. Way to view mortality – a survivor curve (# of survivors plotted against age).
** Population Growth Rate.
Birth rate – Death rate (14 births/1000/y – 8 deaths/1000/y)
Growth is 6/1000/y or 0.6%/y.
** Sex Ratio – refers to male to female ratio. It influences Growth rate. Sex ratio is not
applicable when an organism has both sexes in one body, example: earth worms.
In polygamous species, the # of females are most important but in monogamous species,
both male and female are important.
In the US, 106 males are born to every 100 females, but by the mid 20s the number
equalizes.
** Age Distribution – The # of individuals in each age group influences the population
growth. Human population has a long life span, and is divided into:
Pre-reproductive
Reproductive
Post- reproductive.
If there was no immigration, the US population as in Italy would be declining.
** Population Density and Spatial Distribution – expressed in # of individuals/unit area.
As numbers increase, competition for resources intensifies, which leads to dispersal.
Emigration resulting from seasonal employment or increasing reproduction may also lead
to dispersal.
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Immigration may introduce characteristics or change culture or have an impact due to
diseases.
Summary of factors that influence Population growth rates.
Populations have a natural, inherent tendency to increase. At the lowest level, number of
females and age distribution are most important.
Population Density can cause immigration.
7 – 2. A Population Growth Curve
Each species has a biotic potential. Growth follows a pattern – Lag, Exponential, and
Stable Equilibrium phase followed by a Death Phase.
7 – 3. Factors that Limit Population Size.
Populations cannot increase indefinitely. There are Limiting Factors (Environmental
Resistance).
*Extrinsic and Intrinsic Limiting Factors,
Some factors which control population are extrinsic, such as predators, or lack of
sunshine.
Intrinsic limiting factors include behavoiral changes as a result of over crowding.
*Density dependent and independent Limiting factors.
Density dependent are those that become more effective as the density of the population
increases
Density independent are population controlling influences that are not related to
population density. Usually, they are accidental, extrinsic factors in nature, as a sudden
down pour or early frost.
7 – 4. Categories of Limiting Factors
There are four:
*Availability of raw materials. Generally abiotic (water, fertilizer)
*Availability of Energy. Plants get energy from the sunlight and animals from
food.
*Waste generation and disposal. Does not apply to plants ; can result in the death
phase for animals.
*Interactions among organisms. Important in determining population size,
especially when density becomes very high.
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7 – 5. Carrying Capacity.
Many populations reach a max size, when they reach a stable equilibrium. Carrying
Capacity is a max sustainable size population for an area, may be influenced by a set of
limiting factors as: successional changes, climate variations, fires, nutrients in aquatic
systems, diseases.
7 – 6. Reproductive strategies and Population Fluctuations
“K” Strategists, organisms that reach a stable population as the population reaches the
Carrying Capacity (Density dependent limiting factors).
“r” Strategists are typically small organisms with short lives. They reproduce many off
springs, exploit unstable environments, and are limited by density independent factors.
Many organisms do not fit into any category.
Fluctuations (in populations) may be due to resources available only for a short time. In
“K” strategists, variations in a relatively stable environment can affect the carrying
capacity of the area.
Population Cycles in Northern Regions of the world, may be due to heavy feeding by
herbivores, which causes the plants to produce a toxic substance.
Large herbivore population can also cause the growth of the predator population.
7 – 7. Human Population Growth.
Current human growth is due to increasing carrying capacity by spreading technology,
food production, waste disposal, medicines discovery, etc.
Calculating growth : 70 – growth rate /year.
7 – 8. Human Population Characteristics and Implications.
Economic Development
Developed countries per Capita income is > 10,000 $ US/year. Europe, US expect to
grow 3% by 2050.
Less developed countries expected growth is 52% . Per Capita Income is <$5,000/year
World population may be 8B by 2050. Of which 86% will be from the Undeveloped
areas.
Measuring the Environmental Impact of a population.
Growth is tied to economic development, and it is a contributing factor to nearly all
environmental problems.
Growth has lead to famine, political unrest, environmental degradation, water and air
pollution, extinctions and destruction, resulting from resources exploitation.
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Several factors interact to determine the impact of a society on the resources of its
country.
IMPACT = Population X Affluence X Damage due to technology
Some countries can therefore sustain a larger population than others.
The ecological foot print is a measure of the land required to provide the resources and
absorb the waste of a population.
Controlling population will not eliminate environment problems, but can reduce the rate
at which degradation is occurring. It may also improve the quality of life. Poor countries
do not have the money to invest in pollution control, health and sustainable agricultural
practices.
7 – 9. Factors that Influence Human Population Growth.
Unlike other organisms, humans are influenced by biological, social, political, economic
and ethical factors.
Biological Factors.
Demography used to predict growth. Currently, birth rates exceed death rates worldwide.
Some countries with high births and low deaths will grow rapidly (Mexico, Indonesia);
Some with low births and lower deaths will grow slowly (Japan, France).
Political upheaval has caused death rates to exceed birth rates in countries (Russia).
The most important factors in human growth determination are: fertility rate (# of women
and # of children each will bear ) and Age Distribution .
Replacement fertility is 2.1
Less than 2.0 results in Zero population growth
Social Factors
Low birth rates are not to every ones advantage. There are several influencing factors :
 Culture and Traditions determine family size. Traditional role of women – to
marry and raise children. No education/ skills, strong religious input. Contrast
with developed countries, where there is access to education, 1st. marriage is
25-27 years. Breast feeding may continue up to 2 years in undeveloped
countries, which may serve to increase the time between successive births.
 Attitudes toward birth control. The better educated are most likely to have
access to birth control, most important regardless of religion. Also important
is the desire of women to limit family size. Several reasons for a large family
include high infant mortality, and lack of social security.
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Economic Factors
In less developed countries, Children can be given jobs that contribute to the family
economy. In contrast, in developed countries, children may be regarded as an economic
drain.
Political Factors.
Government population Policy has instituted programs that are meant to encourage
people to have children (Hungary, Sweden –paid leave from jobs for mothers)
Tax systems (US income tax laws)
China has taken steps to limit births (fertility rate 1.6)
India has had very little success (Fertility rate 3.0). Plans call for a reduction in infant
mortality, immunization of children, encourage girls to attend school.
Immigration. .Due to work force shortage, some countries encourage immigration. In the
US, one third of the population increase is due to immigration. Canada accepts 300,000
new immigrants per year. (1% of its current population).
7 – 10. Population Growth Rates and Standard of Living.
Appears to be a relationship between growth rate and Std of living.
Standard of living is an abstract concept that attempts to quantify the quality of life (but
various cultures have different feelings for what is desirable).
The Standard of Living factors include:
 Economic well being (GNP/ Purchasing power per person).
 Health conditions
 Ability to change status in the society.
Comparison between US with Argentina and Kenya illustrates this point.
Fertility Rate :
US -2.0 ; Argentina - 2.4 : Kenya - 4.9.
GNI
$39,000
$ 12,460
$1,050
Secondary School access for females 89% :
84%
: 24%.
Malnutrition
1% :
5% :
Life expectancy
78 years ;
74 years ;
Infant mortality
6.6/1000 ;
16.8/ 1000 ;
US $
20%
47 years
77/1000.
7 – 11. Hunger, Food Production, and Environmental degradation.
As the human population increases, the demand for food rises. Grow or Purchase. Small
farms have no surplus monies to buy additional foods. If the crop fails, people starve.
China, 63% of the people live on farms; India, 72%.
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Environmental Impact of Food Production
Each ecosystem has a max biomass that can exist within it. Increase population means
decrease in plants and animals. One gains and one looses.
Mismanagement leads to less production, possibly desertification, extinction, etc.
The Human Energy Pyramid.
As a result of the basic need for food, people in less developed countries feed at a lower
trophic level. – can lead to malnutrition and stunts physical and mental development.
In developed countries, many people suffer from obesity.
Economics and Politics of Hunger.
Net Exporters of food include US, Canada, Australia, New Zealand, and the EU.
Net Importers are Eastern Europe,
China and India export some food.
Food production has increased as a result of improved plant varieties (green revolution)
Some countries (Japan) are net importers, have enough money to buy food and do not
have the malnutrition.
Hunger occurs when food cannot be purchased or gotten from humanitarian aid. In
addition, political activities determine food availability. War, payment for foreign debt,
corruption all contribute to malnutrition.
Area of greatest need is Sub Sahara Africa.
Solving the Problem
Charitable Organizations emphasizes self sufficiency. Is the improved Green Revolution
working (?)
7 – 12. The Demographic Transition Concept.
Countries with the highest Std of Living have the lowest Growth Rate – leads one to
suggest that countries go through a series of stages – The Demographic Transition.
The Demographic Transition Model
The model is based on the historic, social and economic development of Europe and the
US.
1st. stage : High birth and death rates. High death rates due to diseases, famine, etc.
2nd. Stage : Death rates fall, but Births continue to rise due to improved economic and
social conditions
3rd. stage : Industrial economy develops. Birth rates begin to drop.
4th. Stage : Birth and Death rates balance out stabilizing the population.
Applying the Model.
Serious Questions : Higher populations today. Energy and Natural resources no longer in
abundance. No more access to large expanses of unexploited lands.
Undeveloped countries have severe economic drain. Industrialization cannot develop fast
enough to have a significant impact on population growth.
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The model may provide insight into why a population will stabilize. But most countries
will need assistance (funds) in education, birth control and technology in order to make
the transition.
7 – 13. US Population Picture.
Population should be stabilizing but two factors are operating which can cause
considerable change over the next 50 years.
Age Structure and Immigration Policy. Presently growth rate is 1.1%/year, about 0.6%
due to births.
Future – more diversified ethnically.
420 MM by 2050.
7 – 14. What does the Future Hold?
Face the same limiting factors as other species. Four factors , regardless of biological
carrying capacity or cultural carrying capacity.
*Available raw materials- Food is a major problem. Currently, > a Billion people
are mal nourished.
*Available Energy. Presently, all depend on fossil fuels. When energy prices
increase, the poor is put in jeopardy. Must develop new sources of energy and its efficient
usage.
* Waste Disposal. Most pollution is a result of human activity. It is sensible to
clean up the environment.
* Interaction with other organisms. We are not the only species of importance.
Expansion causes the extinction of others, on whom we depend and destruction of others
puts our survival in jeopardy.
* Social Factors Influence Human Population. Humans are social animals who
have the freedom of choice. Decisions are made based on history, social situations,
ethical and religious considerations and personal desires. (emotional).
Philosophers, theologians, politicians and Sociologists develop the strategies.

Ultimate Size Limitation. We will reach the earth’s carrying capacity and
stabilize. Some suggest that we are approaching that point. Others maintain
that we can double the population before that point is reached. If expansion
continues at the present rate, population will double by 2060 (12 B). Recent
studies note that the rate is slowing (9 B by 2050). Lack of food and water or
increase waste may ultimately control the size of the population. Or will
enforced sterilization and economic penalties become the norm?
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Global Perspectives
AIDs Impact. – Population hollowed out.
Elephant Population – 1.3 M in 1980 to 650,000, when the Ban on Trading in endangered
species was instituted.
The Lesser Snow Goose - growth from 800,000 to 4.5 M leading to destruction of the
ecosystem, once the hunting ban was put in place.
Population Control
Canada – bonus /each child
China – family planning
Australia – Immigration
Romania –
South America – religious
Europe – labor import.
Case Study
Mexico growth rate is 2.4%, will double in 30 years, down from 3.5% in 1970.
42% of the present population is < 15 years old and 21% of the economydepends on US
jobs.
Should the US be involved in Mexico’s population policy? And or should the US set
policy that affects Mexico’s problems.
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